Deposition of amyloid in cerebral blood vessels (cerebral amyloid angiopathy, CAA) is a common condition in the elderly associated with both hemorrhagic and ischemic strokes. CAA is also a potentially important model for understanding the pathogenesis of Alzheimer' s disease, the other major beta-amyloidosis of the central nervous system. At the Alzheimer Research Unit at Massachusetts General Hospital, we have used clinical, neuropathological, and genetic approaches to define the pathogenic steps involved in CAA. These studies have been limited, however, by the static nature of post-mortem brain tissue and the two-dimensional nature of single brain sections. The current proposal seeks to move beyond these limitations by using multi-photon confocal microscopy to observe the development of CAA in transgenic mice over time, and by using multi-photon microscopy and computer-aided image reconstruction to analyze the three-dimensional structure of affected blood vessels. We will use these techniques to examine the processes of 1) amyloid deposition in vessels; 2) breakdown of the amyloid-laden vessel wall; and 3) response to anti-amyloid immunotherapy. We will test whether Abeta initially deposits near vessel branchpoints, whether vessel amyloid affects the deposition of parenchymal amyloid, and whether amyloid deposits preferentially on specific vessels. We will generate a timeline of CAA, from the first deposition of A13 species through formation of amyloid, loss of smooth muscle cells and subsequent vasculopathic changes. We will determine whether there are potential detrimental effects to vessels by anti-Abeta therapies. Studies will be performed on mice doubly transgenic for mutant amyloid precursor protein and presenilin- 1, mice that demonstrate detectable CAA at ages as early as six months. Parallel studies on the three-dimensional structure of amyloid deposition and vessel breakdown will be performed on human tissue taken from collected cases of CAA, including the unique Iowa form of familial CAA. Successful completion of these studies will delineate the pathways involved in CAA initiation, propagation, and vessel damage, as well as determine the feasibility of specific immunotherapy for this currently untreatable disorder.